This invention relates generally to load responsive fluid control valves and to fluid power systems incorporating such valves, which systems are supplied with energy from negative system loads.
In more particular aspects this invention relates to load responsive direction and flow control valves capable of proportional control of negative loads, which maintain a constant pressure differential between negative load pressure and valve outlet pressure.
In still more particular aspects this invention relates to pilot operated load responsive controls of direction control valves, which permit variation in the level of control differential between negative load pressure and valve outlet pressure, while this control differential is automatically maintained constant at each controlled level.
Closed center load responsive direction and flow control valves, capable of proportional control of velocity of negative loads, independent of the load pressure, are very desirable. Such valves, by fluid throttling action, automatically maintain a constant pressure differential between negative load pressure and valve outlet pressure. A variable orifice, introduced between the negative load and valve outlet, varies the flow supplied from negative load, each orifice area corresponding to a different flow level, which is maintained constant irrespective of variation in the magnitude of negative load. Such load responsive direction control valves, for control of negative loads, are disclosed in my U.S. Pat. No. 3,744,517 dated July 10, 1973 and my U.S. Pat. No. 3,882,896 dated May 13, 1975. However, while those valves are effective in proportionally controlling negative loads, they provide a constant pressure differential and therefore a constant throttling action across each valve. Such constant pressure differential is predetermined during construction of the valve control and therefore can not be varied during control of negative load. Also those valves use an unamplified load pressure signal, in operation of their controllers, requiring a control signal at a comparatively large energy level.